Have fun with this basic handheld radio direction finder!
HANDI-Finder 
Radio Direction Finder The HANDI-Finder ®


This Radio Direction Finder Device Connects to an FM Receiver, Transceiver, or HT

HANDI-Finder Parts Layout
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the full view layout drawing
from a PDF file

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HANDI-Finder
Radio Direction Finder
Component Layout
The HANDI-Finder®

The HANDI-Finder® is a HANdheld DIrection Finder which can be used to localize both AM and FM carrier-based sources using a single connection to the antenna input of an FM receiver tuned to the frequency of interest in the range of 45 to 450 MHz. It has been designed for bare-bone functionality as well as low power consumption, simplicity, and economy!

Because it is both an easy-to-build kit for the beginner and a convenient basis for further experimentation by those with more experience, it makes a great club project! Overall, it is a quick, inexpensive way to implement the concept of direction finding, and provides something relatively compact to keep readily available for locating sources of interference.

Except for adding a handle, fabrication is minimal. Two open-loop antennas are made from coat hanger wire bent into halves of a "bow-tie" shape and mounted directly to the circuit board, as illustrated in the "layout" drawing.

The coax downlead is connected to an FM receiver and detects the carrier regardless of whether the transmission mode is AM or FM. The unit is switched on (UP) and rotated for a null in the audio tone that it adds to the audio coming out the receiver. The signal direction is perpendicular to the plane of the antennas. There is 180-degree ambiguity, but this is not a problem in actual use because multiple "bearings" must be taken anyway in order to establish a "fix" on the location. Once close in, the operator works toward the general sense of the direction, and again the ambiguity is not a problem.

The 3-position switch is moved DOWN to stop the tone but still keeps the antenna activated for monitoring and standby purposes, --or it is moved to the CENTER position to shut off the unit. Refer to the extensive discussion in the manual which describes construction variations, and the concepts behind the design.

"Build the HANDI-Finder" appeared as an article in QST Magazine, May, 1993.  All the information in that article and much more is included here! By clicking on the appropriate boxes in this web page, all the drawings and text that come with the kit can be printed out or downloaded from PDF files.  You can copy the layout and build one on perfboard!  All parts are available from sources like Digi-Key and Mouser.

It should be noted that this is an experimenter's kit that starts out simple, but can get more complex as one expands on the principle to get better performance. Generically, this is known as a TDOA, Time-Difference-Of-Arrival detector. Time/phase-difference detectors of this sort are susceptable to multipath, which is often overwhelming!  The simple configuration can be quite acceptable on lakes or flat open land. However operation in the vicinity of hills, buildings, or dense forest can be quite problematic due to multipath.  Here, a combination of techniques such as using the circuit in combination with two spaced beam antennas can be much more effective, but also much more bulky! Also note that since this scheme detects a carrier-based signal source, it cannot be used to localize random noise sources!


HANDI-Finder® Experimenter's Kits
may be obtained by contacting:
Northern Ohio Amateur Radio Development
P. O. Box 271
Brunswick,  OH  44212-0271  USA

Tel: 330-225-7373   www.noard.com

Click here for prices and order info

Only complete, packaged kits may be ordered.
Problems with defective or missing parts are promptly addressed.

Click here to open an HTM file that will allow you to read the Instruction Manual on screen. You can then select "File" in your viewer, check "print preview" and "print" (8pages) if you wish .

DO NOT CLICK on any "Active-X" or other instructions that may open at the top of the screen. --Let us know if you cannot read the manual!


Click here for quick full-size
view of the SCHEMATIC


Click here to open a PDF file
that will allow you to read, print,
and download the SCHEMATIC
Click here to open a PDF file
that will allow you to read, print,
and download the Kit Parts List

This is the official website for the "Original" HANDI-Finder® which was described in QST Magazine, May, 1993

The components described in the parts list are compatible with, and properly fit, those circuit boards which have the official "HANDI-Finder" and RALTEC trademarks. The components and approved circuit boards are sold only as complete kits and not available separately, except for warranty purposes.

Please tell us how you discovered this website, and what you would like to see added to it.  Perhaps you have interesting experiences using the HANDI-Finder® that you would like to share with others.

This page was last updated Apr 18, 2011.

  


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RALTEC® and HANDI-Finder® are TRADEMARKS registered with the U.S. Patent and Trademark Office




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